Low-impact development and wetlands protection

One-line orientation

Low-impact development manages rain near where it falls so the finished site handles water more like the undeveloped site. Wetlands and floodplains are separate regulated areas that also constrain site planning.

Key points

• LID philosophy: mimic pre-development hydrology — manage stormwater at the source by infiltrating and filtering it rather than collecting and piping it off site.
• LID techniques:
  • Permeable / porous paving — lets water soak through paved surfaces.
  • Bioretention / rain gardens — planted depressions that collect and infiltrate runoff.
  • Green roofs — absorb rainfall and slow runoff at the top of the building.
  • Bioswales & added green space — vegetated conveyance that also filters and infiltrates.
• Infiltration vs release-control: LID is infiltration-first (reduce the volume leaving the site). A detention pond is release-controlled (store, then meter outflow). Different philosophies — soak in vs slow down.
• Wetlands: ecologically sensitive, strictly regulated; filling generally requires replacement/mitigation elsewhere. They constrain site planning and construction.
• Floodplains: flood-prone areas with their own (separate) regulations — also a key planning constraint, distinct from wetlands.

Confusions / comparison

	LID (infiltration)	Detention (release-controlled)
Core move	Soak water in at the source	Store then meter outflow
Goal	Mimic pre-development hydrology; cut volume	Cut peak flow rate downstream
Examples	Permeable paving, rain gardens, green roofs	Detention basin + restrictor outlet

Protected land	What it is	Planning effect
Wetland	Ecologically sensitive, regulated	Fill → must replace/mitigate elsewhere
Floodplain	Flood-prone in major storms	Separate regulations; siting constraint

Related

→ Runoff strategies (this module): shallow-site infiltration tools · Detention vs retention (this module): the release-controlled alternative · SWPPP & erosion (this module): construction-phase counterpart · Site slopes (this module): grades that enable infiltration.